Non-polypoid adenomas of the colon are associated with subjacent lymphoid nodules - An experimental study in rats

Background: Subjacent lymphoid nodules (SLNs) have been found in 38% of non -polypoid colonic adenomas in humans. In the present work the presence of S LNs in experimentally induced colonic adenomas was investigated in rats. Me thods: 1,2-Dimethylhydrazine was injected subcutaneously in 290 Sprague-Daw ley rats for 27 weeks. Results: An SLN was present in 28.6% of the 84 adeno mas, in 8.4% of the 119 adenocarcinomas, and in 9.7% of the 31 small carcin omas without remnant adenomatous tissue. An SLN was found in 35.6% of the 5 9 non-polypoid neoplasias but only in 9.1% of the 175 polypoid (that is, ex ophytic) neoplasias. When only adenomas were considered, SLNs were present in 50.0% of the 31 non-polypoid adenomas but only in 14.0% of the 50 polypo id adenomas. Conclusions: Non-polypoid colonic adenomas evolve preferential ly from the minimal fraction of the colonic mucosa that overlays the few ex isting lymphoid nodules in rats.